We study in detail a scenario in which the inflaton scalar field couples to both a visible sector (VS) and a hidden sector (HS). The VS is assumed to contain the Standard Model (SM), while the HS contains a dark matter (DM) candidate. We are in particular interested in a scenario in which the inflaton decays dominantly into the HS degrees of freedom. The DM candidate is taken to be a dark Dirac fermion $χ$, coupled to a massive dark photon $γ'$, a popular model for a HS also known as Dark QED. The inflaton decays into particles of both sectors generate an initial asymmetry between the SM and HS fermion abundances, which we model as being proportional to the ratio of effective Yukawa couplings, $y$ and $y'$. We pay particular attention to the process of thermalisation of the HS, with temperature $T'$, as a function of $y'$ and $α'$, the HS fine structure constant. We investigate the several possible ways of producing the observed DM relic abundance, and their interplay with the reheating of the HS and the transfer of energy between the HS and the VS. Key results, beyond the systematic character of our analysis, include: a new mechanism for DM production, which occurs when DM particles annihilate while still being produced by the inflaton decay; a study of the temperature ratio $ξ= T'/T$ and its relation with the initial energy asymmetry between the HS and VS, as parameterized by $ξ_i = \sqrt{y'/y}$; a reassessment of the domain of viable DM candidates, taking into account the constraints set by unitarity and the thermalisation of the HS, accounting for the LPM effect; and, in cases where the HS does not reach thermal equilibrium, an analysis of how non-thermal DM production fits within the domain of thermal DM candidates.
Genesis of baryon and dark matter asymmetries through ultraviolet scattering freeze-in
Institute for Fundamental Science and Department of Physics, University of Oregon（俄勒冈大学基础物理研究所与物理系）；Center for Theoretical Physics – a Leinweber Institute, Massachusetts Institute of Technology（麻省理工学院莱因韦伯理论物理中心）；Department of Physics, Harvard University（哈佛大学物理系）；TRIUMF（特里尔姆夫国家粒子加速器中心）；Department of Physics and Astronomy, University of California, Riverside（加州大学河滨分校物理与天文系）
